The research proposed in this application is designed to give a rigorous test of the transport aspects of the Chemiosmotic Hypothesis (Mitchell) and particularly of the notion that transmembrane transport of hydrogen ions is the critical factor in transfer of metabolic energy to a wide variety of different transport processes The fungus Neurospora crassa has been chosen for these experiments both because it permits direct measurement of all the parameters required to specify a transport system: membrane potential, membrane resistance, net and unidirectional fluxes of ions and uncharge substrates; and because it admits manipulation of these parameters by standard genetic techniques. The principal immediate objectives of the research are 1) to define the current-voltage relationships for particular transport system in the plasma membrane: for the electrogenic H ion extrusion system, for one or more H ion-dependent cotransport systems, and for the difsusional leak. 2) To study in detail the dependence of substrate transport (e.g., glucose uptake) on H ion-transport and on membrane potential. 3) To explore the mechanisms of action of certain lipid-soluble ions and ion solubilizing antibiotics, whose behavior in intact eukaryotic cell membranes is clearly more complicated than in artificial membranes or in membrane vesicles prepared from organelles or from prokaryotic cells.